Multiple myeloma (MM) is characterized by accumulation of malignant monoclonal plasma cells in the bone marrow. Median overall survival (OS) is 3 to 4 years but varies widely between patients. Currently, the International Staging System (ISS), based on serum β2m and albumin is clinically widely used to classify MM patients into three prognostic categories. [1]
Based on cytogenetics, two classes of MM can be distinguished with implications for MM biology and prognosis. Hyperdiploid MM, ˜60% of patients, characterized by trisomies of multiple odd chromosomes (3, 5, 7, 9, 11, 15, 19, and 21) has a relatively good prognosis. Non-hyperdiploid MM, ˜40% of cases, is characterized by recurrent translocations involving the immunoglobulin heavy chain gene at 14q32, resulting in transcriptional activation of CCND1, CCND3, MAF, MAFB, or FGFR3/MMSET. [2, 3] Translocation t(11;14), involving CCND1, confers a relatively favourable prognosis whereas translocation t(4;14), involving FGFR3 and MMSET, has poor prognosis. [4, 5] The translocations t(14;16) and t(14;20), involving the MAF oncogenes also confer a poor prognosis, although recently this has been debated [6]. In addition, del(17p), del(13q) and 1q-gain detected with conventional karyotyping were reported to be associated with poor prognosis. [7]
Based on gene expression analysis, a number of classifications for MM have been published which include the University of Arkansas for Medical Sciences (UAMS) classification and more recently a classification by our own group. The UAMS molecular classification of myeloma consists of seven distinct gene expression clusters, including translocation clusters MS, MF, and CD-1/2, as well as a hyperdiploid cluster (HY), a cluster with proliferation-associated genes (PR), and a cluster characterized by low percentage of bone disease (LB). [8] Our classification of MM resulted in three additional clusters: NFκB, CTA and PRL3. [9]
Gene expression is able to explain an even larger amount of variance in survival compared to ISS and cytogenetics. One of the first survival signatures based on gene expression was the UAMS-70-gene classifier, and the further refined UAMS-17-gene classifier. [10, 11]. Other classifiers include the Millennium signature, the MRC-IX-6-gene signature, and the IFM classifier. [12-14] In addition signatures were reported to predict plasma cell proliferation such as the recently published gene expression proliferation index (GPI). [15]
The aim of this study was to develop a prognostic signature, based upon gene expression profiles (GEPs) of MM patients, treated with either standard induction treatment or bortezomib induction, followed in both cases by high-dose melphalan and maintenance.